Recording and reproducing of sound



Nov. 11, 1952 A, KAROLUS ETAL 2,617,891

RECORDING AND REFRODUCING OF'SOUND Filed July 7, 1948 2 SHEETS-SHEET 1 And e Henry.

Inventors [Guolus HP Erna Hambu g A. KAROLUS ET AL RECORDING AN D REPRODUCING OF SOUND Nov. 11, 1952 2 SHEETSSHEET 2 Filed July 7, 1948 Inverdlors 'I: Karolus Erna Harnb Aug'us urg'er H1-Lclre Henry.

Patented Nov. 11, 1.952

RECORDING AND REPRODUCINGOF SOUND August Karolus, Zollikon/Zurich, and Erna Hamburger and Andre Henry, Yverdon, Switzerland, assignors to Paillard S. A., a corporation of Switzerland Application July 7, 1948, Serial No. 37,356 In Switzerland July 10, 1947 TS'Claim's. 1 t

The present invention relates to sound records and improved apparatusand processes for the recording and reproducing of sound. 5

In the sound film art, the sound phenomena are recorded as 'phonograms on a carrier strip which unreels at a constant rateior speed. The

sounds or sound henomena, of whatever kind, are generally recorded upon the strip in the form of slit images which. follow one another in the direction of motion of 'the strip.

Depending on whether the lengthjof the image or its degree of transparency'is the variable factor, a distinction is made between (a) The variable area or fixed density proc- 'ess, and t (b) The variable density process.

Generally speaking, and regardless of what process is used, the higher the quality required of the sound record, the more difiicult it is to carry out the photographic process as a whole.

As a matter of fact, it is well known that the non-linear distortions which cause the app arance of harmonics, the formation of sounds through interference; and undesirable detection efiects, are due chiefly to the fact that the characteris'ticof photographic reproductions is not linear. l V a The problems of eliminating distortions and of high fidelity reproduction of the sound volume are extremely difficult to solve with theknown processes, the more so since a better volume range in the reproduction, i. e., an increased range for the intensity variations of the reproduced sound,

entails still greater distortions.

Various methods aiming at obtaining higher sound fidelity have made it possible to extend the sound volume range to a certain extent while keeping distortions and background noises at an acceptable level.' But these methods have not proved satisfactory for the perfect reproduction of music, for instance.

The process hereinafter described represents a considerable improvement in the recording of :sound on strips used either for direct reproduction, or for printing on fi1m, or for reproduction on paper. To obviate the aforementioned 'difiiculties, the instantaneous value of the amplitude of the sound-wave is represented by the respective position of the images of a slit which follow one another at intervals of time shorter than the duration of half a cycle of the highest sound to be recorded and not, as heretofore, by their length or transparency. Thus, in reproducing. the record, the impulses representing the sound wave to be reproduced are identified solely by their respective positions, so that neither their degree of opacity nor the non-linearity of the characteristic of photographic reproduction plays any part in the process. 1

It W111 thus be understood that, ma res ent invention, any variation inthe opacity of the slit images has ,no' bearing on the reproduced sound phenomenon. Amplitude, limitation renders the process absolutely independent of fortuitous variations in the opacity of. the images that may occur during rec'ordingor printing, and of variations in the intensity of tlie light that may occur during reproduction. e

However, when frequency modulation is used, it is desirable to provide a carrier wave whose frequency is much higher than the highest audible frequency to be recorded. Therefore; in theusual type of recording where the images suc ceed one another in the direction of motion of the strip, the unreeling speed of the strip and the diameter of the reels are such as 'toirende'r manipulation extremely difficult and the con-- sumption of material prohibitive; In the process hereinafter described it is proposed to avoid these drawbacks by using a known process, namely, transverse scanning, in which a "series of images arranged in rows ap reximatelyf perpendicular to the direction of motion of the strip,

are recorded on the latter, 'The scanning speed corresponds then to the recording messed the unre'eling' speed of the film is substantially reduced. I I I The present invention ha s forone' of its objects the provision ofdevices for recordin and reproducing sou nd phenornena, in which; arectilinearly and uniformly moying carrier strip receives an image, and is scarined,,resrectively, by means of .a beam of light passing t roughma slit. These deyices differ from the knownron'es in that the light beam is. o tically riontro led in rhythm with a frequenc -mddulated c rr er wave, the instantaneous frequency of thecarrier wave being characterized by the instantaneous value of the sound wave, thebear'ri thnsuinorlu device for the optical modulation of a light beamby this frequency-modulated Wave. Still another device is provided for photographically recording upon the strip, this being achieved by optical deviation of the light beam, preferably perpendicularly relative to the direction of motion of the strip.

The carrier strip for recording sound phenomena obtained in accordance with the aforementioned device, is characterized by the fact that the strip carries a succession of slit images of the same dimensions and the same opacity and which, in the non-modulated state, follow one another at equal distances corresponding to the mean frequency of the carrier wave and which are influenced by the sound phenomena in such a way that their instantaneous frequency corresponds to the instantaneous value of the sound wave, and by the fact that the rows of successive slit images form an angle, in other words, are arranged preferably transversely relative to the direction of motion of the strip.

Preferred ways of carrying out the invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which Figure 1 is a plan of recording apparatus in which frequency modulation is employed,

Figure 2 is a plan of reproducing apparatus for reproducing sounds from the records produced with the apparatus of Figure 1,

Figure 3 is a plan of scanning apparatus,

Figure 4 is a section on the line IVIV of Figure 3, and

Figure 5 illustrates a portion of another form of reproducing apparatus.

Referring to Figure 1, the recording apparatus here illustrated comprises an electrical audiofrequency generator S such as a microphone for example, feeding a low frequency amplifier ABF controlling a frequency modulator M, a light modulator ML controlled by the frequency-modulated tension issuing from a power amplifier AP, an optical system 0 and a scanning device B serving to record upon a film F a series of images of a slit which succeed one another in rhythm with the frequency-modulated tension.

The modulation of the light may be achieved with the aid of either gas discharge lamp, such as, a high pressure mercury lamp or Kerr cell or a supersonic valve functioning on the Debye- Sears effect. See U. S. Patent No. 2,084,201. These devices permit strong light intensities to be modulated with good output up to 100 kcs.

In order that the images on the film may be well-contrasted, the signals may be transformed, with the aid of any known or suitable device, into signals of rectangular wave-form.

The reproducing apparatus illustrated in Figure 2 comprises a source of light 0' of constant intensity, a scanning device B with which a beam of light from the source 0' is swept periodically and transversely across the film record F and a photo-electric cell I3 which collects light passing through the record.

Current originating on the anode of the cell and which is in the form of impulses succeeding one another in the rhythm of the modulated frequency, is amplified by an amplifier A. The voltage thus obtained traverses in succession an amplitude limiter LA, a discriminator D and a detector DE. The detected current, after amplification in a low frequency amplifier BF is finally used to energise a loud-speaker HP.

The alternative form of sound head illustrated in Figure 5, comprises a combined photo-electrio cell and electron multiplier 13, with the aid.

of which electrons emitted from a photo-electric substance are multiplied, thereby enabling. one or more of the amplifying stages represented by A to be dispensed with, and diminishing ground noise.

The reproducing apparatus described above, is

intended for reproduction by transmision of light through a film, as distinct from reproduction by reflection, and is suitable for use with records on ordinary transparent film or with records printed on strips of cellophane. But the record may be transferred to a strip of paper by impression or photographic copying. Such records on opaque films are explored by means of refiected light, with the aid of any of the known devices in everyday use in television. In such a case, the scanning device hereinafter described for reproduction by transparency, needs to be modified only in details of construction in order to render it suitable for use with opaque records.

Figures 3 and 4 illustrate scanning apparatus with which the film can be scanned transversely, that is to say, substantially perpendicularly to its direction of motion.

This scanning device comprises a platform 9 rotatably mounted on an axis 2| and rotated by an electric motor (not shown). The plane of rotation of the platform 9 is parallel to the plane of the film F which runs between two sprockets [2 having teeth l9 engaging perforations 29 in the film to draw it along at constant speed.

The platform 9 carries a plurality of equiangularly spaced lenses [0 the optic axes of which are all parallel to the axes of rotation 2 l.

Also fixed on the platform 9 are a plurality of mirrors ll one of which faces, and cooperates With, each lens I0. Each mirror is inclined at 45 to the plane of the platform and the normal to the centre of each mirror intersects the axis 2|.

The several mirrors ll thus substantially envelop the surface of a frustum of a cone and within this frustum is located, separate from the platform 9, a fixed source of light 1 within a housing 22 formed with an aperture 23 opposite which is located a condenser lens 8 concentrating the light issuing from the source 1 through the aperture 23, upon a slit 6 located precisely on the axis 2|.

This scanning device functions in the following way:

Light rays emanating from the source I and passing through the aperture 23' are concentrated by the condenser 8 upon the slit 6 so as to form a conical beam of solid angle a measured perpendicularly to the axis of rotation 2|.

When the film F is set in motion at a constant speed in the direction of the arrow 2 and the platform 9 is rotated at a constant speed, the beam of rays passing through the slit 6 falls in turn upon each of the mirrors ll, each of which reflects the beam along the optic axis of lens is cooperating with it. This lens Iii concentrates the light as a beam 3 onto the film F. Since the optical element constituted by a mirror H and a lens It is moving at a constant speed, and the mirror H intercepts only that part of the beam. which traverses the slit 6, it will be appreciated that the beam of rays 3 issuing from the lens l0,

. moves with the two-part optical element constituted by a mirror H and a lens Ii].

The beam of light 3 describes an arc of a circle the angular length of which corresponds approxsmel l'matelyw t the angles of the beam of ra s em" ins :mmtne slit ia d hus an he ,film erpe u rl to it d rection o it menhi whilst the opt caldemen ie the mirr r 3H and lens 1.0, p o ect 1 1101 the fi m F a s anning spot which is" an image of the ,slit 6.

A .a esult .Of he un f rm r c il n ar movement Of the film and th tran verse s a nin of th beam th ima s uc don th fi m mo ver it alon "an arc t e cho d o which i Pbli uely c i ed wit res t to t ,lcnsilt d e mlzaxis "o the filmsuallv he hord y co nc de wi h t ra e d rect on- A lth p atiqlm 9 e a e y cn' ant s e d. heieleme t Al .H in urn ent t e b am mer in irom the s t 5, nd e ch e ment iellts noon th film a resh r w oflmases o the slit The an a of th s b am c siwnsls h 'an leeena atm two neighbo n m o s 1 I; .5 th t ne mi r enters he b m of ay em in mm he s t asth e d n m rq leav s t It follows that during a short space of time,

co res ndin w h ha ta b h platform 9 o pa throu h t e a u a l n t o a m r r. two topi a1 elements ll, p oje t a i ag simultaneously upon the film. Thusthere'is a nd of overla p n W en the irst few" images" of one row are" being recorded (or', reproduced) simultaneously with the last few images of the next preceding row, and these two'groups of images may be said to be isochronfal. The optical system as'awhole is so designed that, during reproduction, the sum of the light falling on two "elements simultaneously is constant and at all times equal to the whole o f-the light falling on one elementworking singly. Discontinuities are thus avoided.

The above described process of recording possesses several advantages. In the first place, if 1 one assumes, by way of example, that the film has a width of 7.5 cm. and that the recording speed is 4.5 m./se-c., it may be easily calculated that the film must be scanned 60 times per second. If now the image of the slit 5 on the film has a height of 1 mm., the minimum speed of motion of the film in order to avoid an overlapping of the rows of images is 6 cm./sec.

This speed is small'in comparison with the speeds hitherto considered necessary for longitudinal recording. Consequently, the present process facilitates editing, for example the finding of a passage, since the length to be unwound is shorter. In order still further to facilitate such a search figure-s, perforations or marks can be provided on the edge of the film. 'The marks may be placed on the film by luminous impres: sion, or'by mechanical or manual impression and may be eiiected entirely automatically.

If one'assumes'a recording speed of 4.5 m/sec. and an image width of 0103 -min ,frequencies up to 70 kcs. can berecorded; Frequency modulationmust then beeffect'ed {on a carrienwave' the frequency or which must be selected to be as low as possible, since the scanning speed and film consumptionare proportional thereto' In order that the frequencymodulation may produce the best results with re'spct'to the ground noise level, it'is necessary that th'frequency deviation shall be at least twice as great as the highest audible frequency to be recorded. If, for examplaa low frequency high limit or? kcs'is chosen, 'thena carrier-wave or sores; and a variation sti e r use h steers-"- ease ill felil per cm. of recording then varies, in accordance with the audible frequency, between Zg =78 images/cm.

and

%g 144 images/cm. i. .e. around a mean value of 5 11 l images/cm.

v In addition to changing position with reference to the normal equidistant positions, the

imagesmay also vary in size, the images remote from one another being larger than neighbouring ones. This is the case, for example, when frequency modulation is employed, but is only a secondary effect which does not occur when, for example, modulation by impulse is employed,

The values and figures indicated above are given only byway of example in order that the best form of the invention known may be under stood. When using optical systems of high quality and employing ultra-violet rays, for example, for the recording, it is possible to obtain much finer images, so that a speed of movement of 4 .5 m./s ec., indicated above, must not be considered as the minimum limit of the recording speed. Furthermore recordings of a much more extensive range of sound waves and utilising a much greater frequency variation may be a hi veddevice for transverse scanning has been described herein by way of example, but it will be appreciated that any other television scanning devices, for example a mirror drum, may be adapted for transverse recording and exploration of a film F. The source of light and the whole of the scanning device may also be replaced by,

or consist of, a cathode ray tube. Such a device provides a very simple way of scanning the film transversely; for the ray may be deflected linearly at the desired rate and may be simultaneously electrically modulated.

' When films are employed certain difliculties may arise from their shrinking. These difficulties may however be easily obviated by providing a device with which the radial position of the lens Iiimay be adjusted. In fact, by modifying the radial position of the optical elements In, H, the curve of the arcs traversed by the exploring beam may be varied and thus made to conform to the curve of the arcs on the film after shrinking.

In the case where the scanning device cornprises a mirror drum, shrinkage may be compensated for by slightly altering'the distance sepgrating t e d um ro h fi m- "We shim: M

la d vi e or rec in sou d data (30 111 1 1- in r tatable m mb r ha ing a p u li o ilsll hfs enilell s ac l s a stat r eph asmal nell wit the ax of a on of said member sa d dia hra m havin a s i a rtu e th rehrash; a. t n ry l ht o rc on one si e 9 sa d S t me n a d r ctin llsht passing hlrgl sh ale s i u ce s el hr lsh said e e as said rotatable member rotates, a photosensitive strip for receiving ri ht pas in through said lenses, and meansfof supporting and moving said film radially'relative to said rotatable member;

2. A device as definedjby' claim 1 in which the lenses'ai e so spaced relative to the lightpassing through the slit that when the axis of the light beam bisects the central angle 'of a pair of con- 7 secutive lenses, some of the light therefrom will pass through both of the lenses to form isochronal images of the slit on either side of the strip.

3. A device as defined by claim 1 having means for radially adjusting the position of lenses on the rotatable member.

4. A device for reproducing sound from a strip containing sound data comprising a rotatable member having a plurality of circumferentially spaced lenses, a stationary diaphragm aligned with the axis of rotation of said member, said diaphragm having an aperture therethrough, a stationary light source on one side of said diaphragm, means for directing light passing through said aperture successively through said lenses as said rotatablemember rotates, means for supporting and moving said strip radially relative to said rotatable member to receive light passing through said lenses, photoelectric means for receiving light from said strip and means for converting electrical impulses generated in said photoelectric cell into sound.

5. A device as defined by claim 4 in which the photoelectric cell is of the type which emits electrons and in which the emitted electrons are multiplied by secondary emission.

6. The combination as defined by claim 4 having means for radially adjusting the position of the lenses on the rotatable member.

'7. In a device for recording sound phenomena, the combination of means for moving rectilinearly and uniformly a photosensitive carrier strip, means for scanning said strip substantially transversely of its direction of motion with a beam of light, a light modulating device, means for controlling said beam by said modulating device, means for producing an electrical carrier wave to excite said modulating device, means sensitive to the sound phenomena to be recorded for modulating the frequency of said carrier wave, whereby the photosensitive strip will record lines containing each a multipilicity of rectilinear slit images of substantially uniform height and opacity and the distance between two successive slit images in a line on the strip in the direction of scanning will be a function of the instantaneous intensity of the sound phenomena.

8. In a device for recording sound phenomena as defined by claim '7, the axis of th scanning means being perpendicular to the plane of the photosensitive carrier strip.

9. In a device for recording sound phenomena as defined by claim 7, the axis of the scanning means being parallel to the plane of the photosensitive carrier strip.

10. In a device for recording sound phenomena, the combination of means for moving rectilinearly and uniformly a photosensitive carrier strip, means for scanning said strip substantially transversely of its direction of motion with a beam of light, a light modulating device, means for controlling said beam by said modulating device, means for producing an electrical carrier wave to excite said modulating device, means sensitive to the sound phenomena to be recorded for pulse modulating said carrier wave, whereby the photosensitive strip will record lines containing each a multiplicity of rectilinear slit images of substantially uniform height and opacity and the distance between two successive slit images on the line in the strip in the direction of scanning will be a function of the instantaneous itensity of the sound phenomena.

11. In a device for recording sound phenomena,

the combination of a rotatable member having a plurality of circumferentially spaced lenses, a stationary diaphragm having a slit aperture therethrough, a stationary light source on one side of said slit, means for directing light passing through said slit successively through said lens as said rotatable member rotates, means for supporting and rectilinearly moving a photosensitive carrier strip radial to said rotatable member in the path of light passing through said lenses, a light modulating device, means for controlling said beam by said modulating device, means for generating an electrical carrier wave to excite said modulating device, and means sensitive to the sound phenomena to be recorded for modulating the frequency of said carrier wave, whereby the photosensitive strip will record lines containing each a multiplicity of slit images of substantially uniform height and opacity and the distance between two images in a line on the strip in the direction transverse of the strip will be a function of the instantaneous intensity of the sound phenomena.

12. The combination as defined by claim 11 in which the lenses are so spaced relative to the light passing through the slit that when the axis of the light beam bisects the central angle of a pair of consecutive lenses some of the light therefrom will pass through both lenses to form isochronal images of the slit on either side of the strip.

13. In a device for reproducing sound phenomena from a transparent strip containing sound data in the form of transverse lines of substantially parallel and rectangular opaque bars spaced from each other, said bars being of substantially uniform height and opacity and their spacing being a function of the instantaneous frequency of the sound to be reproduced, comprising a rotatable member having a plurality of circumferentially spaced lenses, a stationary diaphragm aligned with the axis of rotation of said member, said diaphragm having an aperture therethrough, a stationary light source on one side of said diaphragm, means for directing light passing through said aperture successively through said lenses as said rotatable member rotates, means for supporting and moving said strip radially relative to said rotatable member to receive light passing through said lenses, photoelectric means for receiving light passing through said transparent strip, means for amplifying amplitudelimiting, discriminating and detecting electrical impulses generated in said photoelectric means into an audio frequency signal, and means for transforming said audio frequency signal into sound.

14. A device as defined by claim 13 in which the photoelectric means is of the type which emits electrons and in which the emitted electrons are multiplied by secondary emission.

15. In a device as defined by claim 13, means for radially adjusting the position of the lenses on the rotatable member.

16. In a device for reproducing sound phenomena from a light reflecting strip containing sound data in the form of transverse lines of substantially parallel and rectangular bars spaced from each other, said bars being of substantially uniform height and their spacing being a function of the instantaneous frequency of the sound to be reproduced, comprising a rotatable member having a plurality of circumferentially spaced lenses, a stationary diaphragm aligned with the axis of rotation of said member, said diaphragm having an aperture therethrough, a stationary light source on one side of said diaphragm, means for directing light passing through said aperture successively through said lenses as said rotatable member rotates, means for supporting and moving the said strip radially relative to said rotatable member to receive light passing through said lenses, photoelectric means for receiving light reflected from said strip, means for amplifying, amplitude-limiting, discriminating and detecting impulses generated in said photoelectric means into an audio frequency signal, and means for. transforming said audio frequency signal into sound.

17. A device as defined by claim 16 in which the photoelectric means is of the type which emits electrons and in which the emitted electrons are multiplied by secondary emission.

18. In a device as defined by claim 16, means for radially adjusting the position of the lenses on the rotatable member.

AUGUST KAROLUS. ERNA HAIVIBURGER. ANDRE HENRY.

REFERENCES CITED The following references are of record in the file of this patent:

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